Genetics and Obesity

Excerpt

The obesity epidemic around the world affects not only adults but also children. About 50% of the time, obesity in childhood is carried into adulthood in a phenomenon known as "tracking." Per the latest data from the World Health Organization, the number of overweight and obese children under five years of age is estimated to be close to 39 million. In the United States, 1 in 3 adult Americans is obese, and the Centers for Disease Control has estimated that the prevalence of obesity among children is 19.3% per data from the year 2017-2018. By 2030 some epidemiologists suggest that 20% of the world's population will be obese, i.e., having a body mass index (BMI) of more than 30 kg/m² in adults, or a BMI ≥95th percentile for age and sex in children aged 2 to 18 years. Obesity as a disease itself is multifactorial and occurs due to complex interactions occurring between genetics and the environment.

The Human Genome project was carried out between the years 1990 to 2003 to map out the human genome. Genome-Wide Association Studies (GWAS) have been ongoing since 2007 to help associate specific genetic variations with certain diseases. Around 250 genes are now associated with obesity. The FTO gene on chromosome 16 is the most important and carries the highest risk of the obesity phenotype.

The Genetic Investigation of Anthropomorphic Traits Consortium is the organization involved in furthering research in GWAS. However, genetic mutations alone cannot explain the heritability of obesity perfectly. The concept of epigenetics was introduced to help understand the heritability of obesity better. Waddington first introduced the definition of epigenetics was first introduced in the 1940s by Waddington and subsequently elaborated by Holiday in 1990. However, the modern definition of epigenetics comes from Riggs et al. in 1996. Epigenetics is defined as "the study of mitotically heritable changes in gene expression that occur without changes in the DNA sequence." Epigenetic marks on the genome alter the way each gene is read to produce a distinct phenotype. This provides a better explanation of how the environment plays a significant role in affecting how genes are expressed.

Epigenome-wide Association Studies (EWAS) began in 2013 to map the epigenome and understand the varied expressions of genes in different tissues. GWAS and EWAS have heralded a new era in the study of genetics and obesity.